The present invention relates to the fabrication of three-dimensional objects from computer designs using additive process techniques. In particular, the present invention relates to the rapid manufacturing of three-dimensional objects using fused deposition modeling and jetting techniques.
Rapid prototyping of three-dimensional objects from computer-generated designs is used to form parts for a variety of functions, such as aesthetic judgments, proofing a mathematical model, concept visualization, forming hard tooling, studying interference and space allocation, and testing functionality. Rapid prototyping techniques have also spread into rapid manufacturing markets, where copies of an object are quickly created, and each object exhibits physical properties comparable to objects made from hard tooling.
Rapid manufacturing applications demand a high throughput, a good surface finish, and strengths, toughness, and chemical resistance equaling that of injection-molded parts. To achieve the desired functional qualities, it is desirable to build rapid manufactured objects out of thermoplastic materials, such as acrylonitrile butadiene styrene (ABS), polycarbonate, and polysulfone, all of which exhibit good physical properties.
Fused deposition modeling is a popular rapid prototyping technique developed by Stratasys, Inc., Eden Prairie, Minn., which builds three-dimensional objects from thermoplastics materials. Fused deposition modeling machines build three-dimensional objects by extruding flowable modeling material (e.g., thermoplastic materials) through a nozzle carried by an extrusion head, and depositing the modeling material in a predetermined pattern onto a base. The modeling material is extruded in fluent strands, referred to as “roads”. Typically, the object is formed in a layer-wise fashion by depositing a sequence of roads in an x-y plane, incrementing the position of the extrusion head along a z-axis (perpendicular to the x-y plane), and then repeating the process. Movement of the extrusion head with respect to the base is performed under computer control, in accordance with design data provided from a computer aided design (CAD) system. The extruded modeling material fuses to previously deposited modeling material, and solidifies upon a drop in temperature to form a three-dimensional object resembling the CAD model.
Another technique for building objects from solidifiable materials is known as jetting, which deposits droplets of modeling material from nozzles of a jetting head, such as an inkjet printhead. After dispensing, the jetted material is solidified (e.g., cured by exposing the material to ultraviolet radiation).
The surfaces of three-dimensional objects developed from layered manufacturing techniques of the current art (e.g., fused deposition modeling and jetting) are textured or striated due to their layered formation. Curved and angled surfaces generally have a “stair step” appearance, caused by layering of cross-sectional shapes which have square edge profiles. Although the stair-stepping does not effect the strength of the object, it does detract aesthetically. Generally, the stair-stepping effect is proportional to the layer thickness, and decreases as the layer thickness decreases.
Current fused deposition modeling machines, such as systems commercially available from Stratasys, Inc., build three-dimensional objects having layer thicknesses ranging from about 180 micrometers (about 0.007 inches) to about 760 micrometers (about 0.030 inches) and road widths ranging from about 125 micrometers (about 0.005 inches) to about 1500 micrometers (about 0.060 inches). Thermoplastic materials flow through extrusion tips having inner diameters typically ranging from about 125 micrometers (about 0.005 inches) to about 500 micrometers (about 0.020 inches), at dispensing rates designed to produce the desired layer thicknesses and road widths.
The fused deposition modeling machines generally operate at voxel rates of about 500 hertz (Hz), extruding thermoplastic materials at a dispensing rate of about three cubic inches per hour. The resulting object resolution is generally about 130 micrometers (about 0.005 inches), depending on the object geometry. The high viscosities of thermoplastic materials (e.g., about 500 Poise) and their low thermal conductivities (e.g., about 0.2 watts/meter-EC) generally constrains the extrusion of these plastics through a smaller extrusion tip (to produce thinner layers) while moving the extruder at a higher frequency (to decrease build time).
Jetting techniques of the current art can eject small droplets of material at a voxel rate of about 2 kilohertz (kHz) to about 200 kHz. The thicknesses of jetted layers generally range from about 5 micrometers (about 0.0002 inches) to about 150 micrometers (about 0.006 inches), with a typical thickness before planarization of about 25 micrometers (about 0.001 inches). Accordingly, the resulting object resolution is generally about 50 micrometers (about 0.002 inches), depending on the object geometry. However, known jettable materials do not have the desirable material properties of the extrudable thermoplastic materials. As such, jetted objects are generally less suitable for rapid manufacturing applications. There is a need for techniques that increase the speed and resolution of building three-dimensional objects from materials that exhibit good physical properties, such as thermoplastic materials.